vendor: update buildkit to v0.8

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/golang.org/x/crypto/nacl/sign/sign.go

@@ -0,0 +1,90 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package sign signs small messages using public-key cryptography.
+//
+// Sign uses Ed25519 to sign messages. The length of messages is not hidden.
+// Messages should be small because:
+// 1. The whole message needs to be held in memory to be processed.
+// 2. Using large messages pressures implementations on small machines to process
+// plaintext without verifying the signature. This is very dangerous, and this API
+// discourages it, but a protocol that uses excessive message sizes might present
+// some implementations with no other choice.
+// 3. Performance may be improved by working with messages that fit into data caches.
+// Thus large amounts of data should be chunked so that each message is small.
+//
+// This package is not interoperable with the current release of NaCl
+// (https://nacl.cr.yp.to/sign.html), which does not support Ed25519 yet. However,
+// it is compatible with the NaCl fork libsodium (https://www.libsodium.org), as well
+// as TweetNaCl (https://tweetnacl.cr.yp.to/).
+package sign
+
+import (
+	"io"
+
+	"golang.org/x/crypto/ed25519"
+	"golang.org/x/crypto/internal/subtle"
+)
+
+// Overhead is the number of bytes of overhead when signing a message.
+const Overhead = 64
+
+// GenerateKey generates a new public/private key pair suitable for use with
+// Sign and Open.
+func GenerateKey(rand io.Reader) (publicKey *[32]byte, privateKey *[64]byte, err error) {
+	pub, priv, err := ed25519.GenerateKey(rand)
+	if err != nil {
+		return nil, nil, err
+	}
+	publicKey, privateKey = new([32]byte), new([64]byte)
+	copy((*publicKey)[:], pub)
+	copy((*privateKey)[:], priv)
+	return publicKey, privateKey, nil
+}
+
+// Sign appends a signed copy of message to out, which will be Overhead bytes
+// longer than the original and must not overlap it.
+func Sign(out, message []byte, privateKey *[64]byte) []byte {
+	sig := ed25519.Sign(ed25519.PrivateKey((*privateKey)[:]), message)
+	ret, out := sliceForAppend(out, Overhead+len(message))
+	if subtle.AnyOverlap(out, message) {
+		panic("nacl: invalid buffer overlap")
+	}
+	copy(out, sig)
+	copy(out[Overhead:], message)
+	return ret
+}
+
+// Open verifies a signed message produced by Sign and appends the message to
+// out, which must not overlap the signed message. The output will be Overhead
+// bytes smaller than the signed message.
+func Open(out, signedMessage []byte, publicKey *[32]byte) ([]byte, bool) {
+	if len(signedMessage) < Overhead {
+		return nil, false
+	}
+	if !ed25519.Verify(ed25519.PublicKey((*publicKey)[:]), signedMessage[Overhead:], signedMessage[:Overhead]) {
+		return nil, false
+	}
+	ret, out := sliceForAppend(out, len(signedMessage)-Overhead)
+	if subtle.AnyOverlap(out, signedMessage) {
+		panic("nacl: invalid buffer overlap")
+	}
+	copy(out, signedMessage[Overhead:])
+	return ret, true
+}
+
+// sliceForAppend takes a slice and a requested number of bytes. It returns a
+// slice with the contents of the given slice followed by that many bytes and a
+// second slice that aliases into it and contains only the extra bytes. If the
+// original slice has sufficient capacity then no allocation is performed.
+func sliceForAppend(in []byte, n int) (head, tail []byte) {
+	if total := len(in) + n; cap(in) >= total {
+		head = in[:total]
+	} else {
+		head = make([]byte, total)
+		copy(head, in)
+	}
+	tail = head[len(in):]
+	return
+}